This application claims priority pursuant to 35 U.S.C. xc2xa7 119, to German application 199 57 747.1, filed Dec. 1, 1999, incorporated herein by reference.
1. Field of the Invention
This application provides for the use of certain silicone-polyethers copolymers as surface-active substances in the production of polyurethane foams.
2. Description of the Related Art
The processes employed in the prior art for producing polyurethane foams are differentiated into a number of types. These differences may concern either the chemicals used or the production machines employed. Thus, for example, a distinction is made between batchwise manufacture in boxes or molds and continuous manufacture on various types of foaming machines. Various groups of polyurethane foams can also be differentiated on the basis of the raw materials used and thus the foam types produced.
Thus, for example, rigid foams are, from their property profile and use alone, clearly distinguished from flexible foams, but even within the group of flexible foams, a distinction is made between hot-cure foam and high resilience foam (cold-cure foam). Here, the term high resilience foam refers to a highly elastic polyurethane foam which is formed by reaction of at least one bifunctional polyisocyanate, e.g. tolylene diisocyanate or diphenylmethane diisocyanate, with at least one polyol having at least two hydroxyl groups per molecule and, on average, a high proportion of primary hydroxyl groups. Due to the high content of primary OH groups, the polyols have a high reactivity toward the isocyanates.
In contrast to conventional polyurethane foams, namely hot-cure foams, a high crosslinking density is therefore obtained even during foaming. This has the advantages that the supply of relatively large amounts of energy during curing can usually be dispensed with and that the total time for curing the foams is shortened. However, a disadvantage is that the tendency to form closed-celled foams is increased and the processing latitude is therefore also narrowed. For the present purposes, processing latitude refers to the tolerance limits within which deviations from a formulation are permissible without the risk of not forming stable and simultaneously sufficiently open-celled or easily crushable foams.
For this reason, there is a demand for products having a less pronounced stabilizing character in production processes for polyurethane foams like hot-cure flexible slabstock foam which do not involve less reactive raw materials. In those cases in particular, the property of cell regulation in the surface zones of the foams is an important quality criterion. This is particularly true for molded high resilience foams, but even otherwise a consistent cell structure over the entire polyurethane foam body is desirable. Although at present a certain degree of stabilization is necessary even in the field of high resilience foam, particularly when using high-solids polyols in combination with tolylene diisocyanate mixtures as reactive component, hot-cure flexible foam stabilizers of the prior art, for example, are nevertheless not suitable as foam stabilizers for such processes.
Instead, significantly shorter and less stabilizing copolymers are normally used as foam stabilizers or cell regulators. These are normally either very short, unmodified siloxanes or products which are little modified relative to the siloxane and have pendant low molecular weight polyether substituents or other groups having a low polarity.
This prior art is reflected in a great number of different patents in the polyurethane field. Thus, for example, GB-A-907 971 stated, as early as 1960, that high molecular weight silicone oils cause an excessively large number of closed cells in the foam. For this reason, the patent cited proposes low molecular weight polydialkylsiloxanes having viscosities of from 2 to 9 centistokes at 25xc2x0 C. These then guarantee an improved processing latitude (see column 2, lines 55 ff.). In general, many low molecular weight polydimethylsiloxanes or short polydimethylsiloxanes silicone-containing surface-active substances allows advantageous stabilization or cell regulation in the production of polyurethane foams.
The present invention accordingly provides for the use of silicone-polyether copolymers of the formula I 
where
Rf is a polyether radical of the average formula
xe2x80x94(Y)c[O(CxH2xO)pZ]w,
where
c=0 or 1,
x=2 to 4, with mixtures of the corresponding monomers also being able to be used,
pxe2x89xa70,
w=1 to 4,
Z=a hydrogen atom or a monovalent organic radical,
Y=a w+1-valent hydrocarbon radical which may also be branched,
Rg is an alkyl radical, preferably, having from 1 to 10 carbon atoms, or a substituted or unsubstituted aryl radical,
where
a is from 0 to 20, preferably from 2 to 8, with the proviso that c and p must not at the same time be 0, as surface-active substances in the production of polyurethane foams.
The AB silicone copolymers of the invention can also be used in combinations with one another or with other organic or silicone-containing surface-active substances.
The value of a is, as a person skilled in the art will know, to be regarded as an average value in the polymer molecule since the silicone-polyether copolymers to be used according to the invention are generally present in the form of equilibrated mixtures.
For the same reason, a corresponding preparation by equilibration of siloxanes usually also gives random mixtures of monofunctional, bifunctional and unfunctionalized siloxanes. Even when such a random mixture is used, it has been found that the effects in the production of polyurethane foams are distinctly superior to the property profile of the stabilizers customarily employed. If desired, a product having a high content of AB polymers can also be obtained by methods known from the literature, e.g. by anionic ring opening of hexamethylcyclotrisiloxane. It is obviously also possible for a random mixture obtained by equilibration to be separated subsequently both at the siloxane stage and at the copolymer stage.
The radicals Rg are alkyl radicals, preferably having from 1 to 10 carbon atoms; e.g. methyl, ethyl, propyl, butyl or hexyl radicals, or aryl radicals, with phenyl radicals being preferred in the case of the latter. For ease of preparation and for price reasons, methyl radicals are preferred. Particular preference is given to silicone-polyether copolymers in which all the radicals Rg are methyl radicals.
It is possible to use either one silicone or silicone-polyether copolymer or a plurality of silicones or silicone-polyether copolymers in combination with one another. In the latter case, the products used according to the invention are present in a proportion of more than about 20%, preferably more than 40%, particularly preferably more than 90%, of the silicone-containing substances of the total high resilience foam stabilizer. Here, the short-chain siloxanes or siloxane rings which are well known to persons familiar with this technical field and are always formed in small amounts in the preparation of siloxane chains by, for example, acid equilibration by literature methods owing to the thermodynamic circumstances are not taken into account separately.
The polyethers may comprise ethylene oxide, propylene oxide and up to about 20% of butylene oxide or higher alkylene oxides and contain both hydroxyl groups and ether or ester groups, such as C1-C6-alkyl ether or ester groups, as end groups. Usually, polyether groups in the molecular weight range from about 100 to about 4000, preferably from 100 to 1500, particularly preferably from 200 to 1000, are used, depending on the chain length of the siloxane part. The compounds are prepared as described in the literature for silicone-polyether copolymers, e.g. by hydrosilylation of a double-bond-containing polyether, if desired in admixture with other double-bond-containing polyethers if mixtures of various stabilizers according to the invention are to be obtained. Another possible way of preparing the corresponding Sixe2x80x94OC-linked structures is equilibration catalyzed by iron(III) chloride as is known from the literature, e.g. of chlorotrimethylsilane with cyclic polydimethylsiloxanes. Subsequent reaction of the resulting Sixe2x80x94Cl-functionalized polydimethylsiloxanes with hydroxyl-containing polyoxyalkylene copolymers under basic conditions and subsequent filtration of the amine salts formed and, if appropriate, removal of solvent used by distillation gives the desired block copolymers.